In the modern era, printers for operation with personal computers and other electronic equipment become widespread rapidly in offices and households owing to their reduced price, improved print quality and improved reliability. Accordingly the demand for ink is expanding from household to industrial use. To further improve the quality, color, appearance, definition and shelf stability of printed images, the demand for ink makes a transition from the conventional dye ink to pigment and other inks having a higher level of properties. A wider variety of inks are now available.
Also in the printing and papermaking industries, a transition to aqueous systems is under way in view of current environmental concerns. Since the water-based systems are slow in drying speed and thus slow in manufacturing speed as compared with the solvent-based systems, the water-based systems are always required to catch up with higher speed operation for productivity improvements. Thus ink and paper coating formulations are required to improve their performance so as to comply with high-speed printing or coating conditions.
Under the circumstances, the ink and aqueous paint industries need a surfactant having an ability to reduce the surface tension of water for imparting wetting, penetrating and dispersing properties relative to substrates. The important factor to be considered for a choice of surfactant is a static surface tension when the system is at rest, but a dynamic surface tension when the system is applied at high speeds to meet the demand for higher printing speeds for productivity improvements.
In the prior art, ethylene oxide adducts of nonyl phenol and polyoxyalkylene alkyl ethers are regarded useful as wetting agents and dispersing aids for ink and coating formulations. However, the use of ethylene oxide adducts of nonyl phenol poses a concern because of possible containment of environmental hormones. The polyoxyalkylene alkyl ethers are safe, but have a high foamability to adversely affect pigment dispersion, failing to accommodate high-speed printing.
Patent Documents 1 to 4 propose water-soluble surfactant compositions comprising a polyoxyalkylene alkyl ether and an acetylene glycol surfactant such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol or its ethoxylate. Although these surfactant compositions have improved surface tension reducing, contact angle reducing and foam controlling capabilities, the recent advance in the high-speed printing technology poses a demand for a surfactant composition having further improved pigment dispersing and foam controlling capabilities.
Patent Document 5 discloses a glycidyl ether-capped acetylenic diol ethoxylate. Despite good surface tension reducing, wetting and foam controlling capabilities, its water solubility is insufficient to form a transparent coating formulation, failing to meet satisfactory performance.